USS R-23 (SS-100) was an R-class coastal and harbor defense submarine built for the United States Navy during World War I.

The R-boats built by Lake Torpedo Boat Company (R-21 through R-27) are sometimes considered a separate class from those of the other builders.

A little over a month after commissioning, R-23 departed New London, Connecticut, for her homeport of Coco Solo, Panama Canal Zone.

Given hull classification symbol SS-100 in July 1920, she was based in the Canal Zone, interrupting her service there only for overhaul periods at Balboa and on the East Coast.

She was berthed at League Island until struck from the Naval Vessel Register on 9 May 1930 and sold for scrap in July of the same year.